(a) Field of the Invention
The present invention relates to a photographic lens system for endoscopes to be arranged on the rear of an eyepiece for photographing.
(b) Description of the Prior Art
In an optical system for endoscopes, for example, desinged to transfer an image by using a relay lens system composed of simple convex lens components, curvature of field is apt to be aggravated unlike that in an optical system for endoscopes designed to transfer an image by using an optical fiber bundle. In addition, curvature of field is further aggravated also by the positive cemented doublets having relatively simple compositions and used in the eyepiece arranged for observing the transferred image and a photographic lens system for endoscopes arranged on the rear of said eyepiece as shown in FIG. 1 (wherein the reference symbol E represents the eyepiece and the reference symbol AD designates the photographic lens system for endoscopes).
The negative curvature of field produced by the relay lens system can be cancelled by using an objective lens system having positive curvature of field. Though objective lens systems having the function to cancel the component of curvature of field produced by the relay lens system have already been known, an eyepiece having such a function has not been known yet. When an image is photographed with photographic lens system arranged as described above, curvature of field is aggravated by the eyepiece and photographic lens system, thereby making it impossible to photograph an image favorably.